HELP please with lethargic silkie chick

[LadiesAndJane]

I have a 4 week old silkie chick that quite suddenly is not doing well. She broods with two others who are doing fine.
They have been fed medicated chick starter from the beginning, vaccinated for Mareks disease. Kept warm, and dry. They have been using a brooder plate, and she is spending most of her time under there. She is not actively eating, though will take egg yolk and nutradrench if I give it to her, which I have been doing, every 2 hours or so.
There is no sign of diarrhea. No runny eyes or nostrils, no cough. No sign of injuries or parasites.
What could the explanation be? She seemed fine yesterday, then today not.
I have not experienced this before with my own chicks at this age.
I have with hatchery chicks in the mail, who failed to recover from the trip.
I hatched this one myself from my own birds and she has been a normal lively chick until today.

 

[Eggcessive]

Had she been doing well up to now? At her age, I would worry about possible coccidiosis. What do her poops look like? Is there food felt in her crop?

 

[Eggcessive]

If you have the liquid corid, you can give a boost of a couple of drops of undiluted Corid twice a day in addition otmthe Corid water.

 

[Eggcessive]

You can mix 1.5 tsp of of the powder in 10mlor 2 tsp of water and that is equivalent to the liquid undiluted Corid.

 

[Wyorp Rock]

They have been using a brooder plate, and she is spending most of her time under there. She is not actively eating, though will take egg yolk and nutradrench if I give it to her, which I have been doing, every 2 hours or so.

Good advice from @Eggcessive
Just to add - omit the Nutri-Drench during the course of treatment with Corid.

 

[HappyDuckie]

Could she have been pecked on the head? I know that silkies and other vested birds can be more prone to injuries that way.

 

[LadiesAndJane]

Thank you @Wyorp Rock Here this morning little one is still alive but seems unchanged from yesterday. Was able to give her some concentrated Corid along with the Corid water. Stopped the Nutradrench and just trying to give her eggyolk. She is still not interested in trying to eat anything on her own. Keeping her warm and comfortable. Not sure what else I can do. She has pooped a little, it is loose and it’s mostly white. Figured it’s because she hasn’t had any solid food in the past 24 hours or more.
I’m trying to massage her crop a little bit it’s feels distended, like a balloon. I’m not sure how much is moving through.
I separated her from her two buddies as I was afraid they may start to pick on her.

 

[LadiesAndJane]

Little one just passed. Thanks to those who responded.

 

[Wyorp Rock]

Oh No! I'm sorry to hear that

 

[LadiesAndJane]

Could she have been pecked on the head? I know that silkies and other vested birds can be more prone to injuries that way.

No, I do not think so. Thank you for replying!